1. Field of the Invention
The present invention relates to digital multimedia broadcasting (DMB), and more particularly to an apparatus and method for receiving data broadcasted through a DMB data broadcast channel.
2. Description of the Related Art
A terrestrial DMB technology enables reception broadcast signals while a user roaming. The terrestrial DMB is based on the European-type digital audio broadcasting (DAB) standard, which provides a data service, as well as video and audio services, through a DMB data broadcast channel.
Broadcast protocols for broadcasting data for terrestrial DMB may be largely classified into three types of protocols, that is, a Multimedia Object Transfer (MOT) protocol, a Transparent Data Channel (TDC) protocol, and Internet protocol (IP) Datagram Tunneling. The MOT protocol is used for broadcasting time-independent data, such as a broadcasting Web site or a slide show. Thus, the MOT protocol is one of the most frequently-used protocols for broadcasting DMB data. In detail, the MOT protocol is used to divide DMB data for a data service into an object unit (i.e. into a plurality of object data) and a broadcast the object data with formation information required for forming the DMB data for the data service using the object data, thereby providing a data broadcasting service through a DMB data channel. Therefore, DMB data transmitted based on the MOT protocol include MOT header data and MOT body data corresponding to the MOT header data. The MOT header data contain construction information, such as the size of the MOT data, the service type of the DMB data transmitted through the MOT protocol, etc.
The TDC protocol is used to transmit time-dependent data in the form of a bit stream, which is different from the MOT protocol transmitting data encapsulated in the object unit. One of representative TDC protocols is a Transport Protocol Expert Group (TPEG) protocol used for transmitting broadcasting traffic information or the like.
The IP is used to transmit and receive datagram data on the Internet through IP tunneling. Such data transmission protocols enable various data to be transmitted to DMB reception terminals through a broadcast channel.
However, since the terrestrial DMB is used by a broadcasting system, the terrestrial DMB is transmitted generally in one direction. That is, when providing a data service using a broadcasting signal based on the MOT protocol, a DMB (Digital Multimedia Broadcasting) broadcasting station only broadcasts broadcast data to DMB reception terminals, but has no way of checking whether or not the broadcasted DMB data have been received without any error by the DMB reception terminals. For this reason, the DMB broadcasting station broadcasts the DMB data repeatedly at a predetermined interval during a predetermined period, i.e. during a broadcasting time period of the DMB data, so that each DMB reception terminal can correctly receive DMB data, which have been received with an error, through the repeated broadcasting.
FIG. 1A is a view illustrating the flow of data (MOT data) broadcasted based on the MOT protocol through a data broadcast channel in the terrestrial DMB. It can be understood from FIG. 1A that MOT object data and MOT header data are periodically and repeatedly broadcasted according to a predetermined MOT data transmission period. The MOT data transmission period is determined based on the number of MOT data that are included in DMB data transmitted through the MOT protocol. That is, when one DMB data includes five MOT object data, the MOT data transmission period corresponds to a period of time, which is required for transmitting five MOT body data corresponding to the five MOT object data, and corresponds to a construction information (i.e. five MOT header data).
The MOT body data and MOT header data may be broadcasted in one of two schemes. One of the two scheme is to group/encapsulate all MOT header data for all MOT body data included in one MOT data transmission period into one MOT data (i.e. a MOT directory) and to transmit the grouped/encapsulated MOT directory. The other scheme is to separately transmit each MOT header data. A part “(a)” shown in FIG. 1A represents an example of a scheme for transmitting all MOT header data using a MOT directory, which is a group of MOT protocol headers, and a part “(b)” shown in FIG. 1A represents an example in which MOT header data and MOT body data are broadcasted as MOT object data are transmitted.
Herein, the MOT body data represent actual content data of DMB data, which include a-plurality of MOT object data. The MOT header data include information relating to the size of MOT body data which is the payload of corresponding MOT object data, information relating to the size of MOT header data, a transport ID dedicated for the MOT object data, and additional information about the service type of the DMB data or the like. Therefore, after receiving all MOT header data or the MOT directory, the DMB reception terminal can obtain the original DMB data by re-forming the received MOT body data based on the transport ID, thereby providing a DMB data service to the user using the obtained DMB data.
However, each the MOT object data, that is, each of the MOT headers and MOT bodies typically contains a plurality of main service channel (MSC) data. The MSC data are received through a plurality of packet data or Extend Program Associated Data (X-PAD) subfields from the broadcasting station. Each of the MSC data forming the MOT header or MOT body includes serial information for forming each corresponding MOT object data. For example, MSC data forming the MOT header may have serial information from No. 1 to No. 10, and also MSC data forming the MOT body may have serial information from No. 1 to No. 10. In this case, each MSC data includes information about whether MOT object data formed by using the MSC data correspond to a MOT header or a MOT body, in addition to the serial information.
FIG. 1B is a view illustrating an example of the construction a plurality of MSC data for forming one MOT object data (i.e. one MOT header or MOT body) and packet data or X-PAD data for forming the MSC data. as shown, a DMB reception terminal forms the MSC data using data received through a packet mode or X-PAC mode. Herein, the MSC data include an MSC data group header, which stores information for forming the MOT object data such as a transport ID, a segment number representing a serial number of the MSC data, and the last segment number required to form MOT object data corresponding to the transport ID. In addition, the MSC data group header may include information relating to the number of MSC data required to form the MOT object data.
Accordingly, when having received the MOT directory or a plurality of MOT header data individually, the DMB reception terminal can recognize the number of MOT object data forming data (DMB data) for a DMB data service. Also, the DMB reception terminal can recognize MSC data used for forming the MOT object data in a single transmission period by using the received MSC data group header. Therefore, the DMB reception terminal can check the MOT object data, which are not re-formed due to MSC data and have not been received or received with an error from among MOT object data in the single MOT data transmission period.
Accordingly, the DMB reception terminal checks such MSC data, which have not been received thereby or have been received with an error, so as to receive the corresponding MSC data during a next MOT data transmission period. If the MOT object data are formed by receiving all MSC data without an error during one MOT data transmission period, the DMB reception terminal re-forms the MOT object data, thereby generating DMB data for a DMB data broadcasting service.
As described above, when the DMB reception terminal does not receive all MSC data contained in the entire MOT object data transmitted during a single MOT data transmission period, the DMB reception terminal must wait until the next MOT data transmission period starts.
Meanwhile, the terrestrial DMB is intended to enable the user to receive a DMB broadcast even while the user is moving. However, when the user receives MOT data while he/she is moving, the probability of error occurrence becomes high. Furthermore, it is impossible to guarantee that MSC data, which have not been received or received with error, can be received without an error during the next MOT data transmission period. Thus, according to the conventional data transmission scheme, the DMB reception terminal must repeatedly receive MSC data in every MOT data transmission period until receiving the MSC data of all MOT object data without an error during one MOT data transmission period, thereby significantly reducing the data receiving speed of the DMB reception terminal.